Second external quality assessment of the molecular diagnostic of West Nile virus: are there improvements towards the detection of WNV?

BACKGROUND: WNV epidemics occur worldwide, new WNV isolates were isolated in southern-east Europe belonging to WNV lineage 2. A first international proficiency study on WNV indicted that some laboratories were not able to detect WNV lineage 2 virus genome by their PCR diagnostic assays. Therefore an actual External Quality Assessment with both virus lineages was performed to monitor the improvements in molecular diagnostics. OBJECTIVES: To asses the proficiency of laboratories to detect West Nile virus with molecular diagnostic tests. STUDY DESIGN: A test panel of different WNV isolates and virus dilutions was given to 26 laboratories to test the samples with their routine diagnostic methods. RESULTS: Twenty-one participating laboratories provided 28 data set results. WNV lineage 1 was detected with high overall efficiency of 92% (67.9-100%) but two different WNV lineage 2 strains were detected at lower rates (mean = 73%, 67.9-75%) by the different PCR assays. 93% of the laboratories were able to detect a WNV lineage 1 with a concentration of 1.2×10(4)copies/ml but the detection rate was decreased to 68% for 1.2×10(3)copies/ml. One laboratory generated false-positive result from the non-virus control samples and 29% of the datasets showed false-positive results for non-WNV flavivirus samples. CONCLUSIONS: The WNV EQA showed an improved proficiency of laboratories as compared to the first EQA. However, the data suggest that problems in the detection of both lineages were still present since the first proficiency test was performed in 2006. Further proceedings versus the detection of both lineages are needed particularly for in-house assays.

External quality assessment of cytomegalovirus DNA detection on dried blood spots.

BACKGROUND: Testing for viral DNA in neonatal blood dried on paper (DBS) has proved a valid means of diagnosing congenital CMV infection with both clinical and epidemiological relevance. To assess the quality of the detection of CMV-DNA on DBS in laboratories performing this test a proficiency panel consisting of nine samples with two blood spots on each filter paper was produced and distributed. Six samples were derived from whole blood, negative for CMV DNA and antibody, and spiked with cell-grown CMV Towne in various concentrations (7.3 x 102 - 9.6 x 105 copies/ml), one was a CMV positive clinical specimen (3.9 x 106 copies/ml), and two samples were CMV-negative whole blood. RESULTS: The 27 responding laboratories from 14 countries submitted 33 datasets obtained by means of conventional PCR (n = 5) or real-time PCR (n = 28) technologies. A correct positive result was reported in at least 91% of datasets in samples with a viral load of 8.8 x 104 copies/ml or higher. However only 59% and 12% identified the 9.4 x 103 and 7.3 x 102 copies/ml samples, respectively, correctly as positive. False positive results were reported by 9% of laboratories and in 11% of datasets. CONCLUSION: These results indicate a clear need for improvement of methods as sensitivity and false-positivity still appear to be a major problem in a considerable number of laboratories.